1. Field of the Invention
The present invention relates to an automotive brake-fluid pressure control apparatus employed for example in traction control during acceleration slippage.
2. Description of the Related Art
Conventionally, hydraulic circuits of various types of structure have been proposed as an automotive brake-fluid pressure control apparatus employed for example in traction control during acceleration slippage; in recent years in particular, as shown in for example FIG. 13, a hydraulic circuit has been considered which can realize antiskid control and traction control and so on, and which has a structure driving two hydraulic pumps P1 and P2 with one hydraulic motor MR.
This hydraulic circuit performs traction control on a vehicle of front-wheel drive (FF) of a front-mounted engine, and valves and the like to perform traction control are disposed in a conduit of brake fluid reaching from a master cylinder M/C to wheel cylinders W/C of left and right front wheels FL and FR. Specifically, these are a master-cylinder cutoff valve (SM valve) which cuts off brake fluid from the master cylinder M/C, a reservoir cutoff valve (SR valve) which cuts off communication from a reservoir R on the M/C side to the intake side of the hydraulic pumps P1 and P2, and also electromagnetic-type valves V1 and V2 which perform holding and release of high brake-fluid pressure given to a wheel cylinder W/C.
Accordingly, in a case of executing traction control with this hydraulic circuit (hereinafter described with reference to the FL wheel), braking force was controlled with holding and release of brake-fluid pressure performed by valves V1 and V2 in a state where the conduit had been interrupted by the SM valve. Additionally, normal brake operation corresponding to depression of a brake pedal BP by a driver was made possible after termination of traction control by causing the hydraulic pump P1 to be stopped along with switching to a state wherein the SM valve was communicated, the valve V1 was communicated, and the valve V2 was interrupted.
However, problems such as described hereinafter existed in a case where the respective valves and the like are established in the above-described manner so that normal braking operation can be operated after termination of traction control.
That is to say, high-pressure brake fluid used in traction control must be expelled when the SM valve and the valves V1 and V2 are switched so as to enable normal braking operation after termination of traction control. However, there existed the problem in that time is required to expel the brake fluid, and setup for normal braking operation is delayed. If the SM valve and the valves V1 and V2 are switched in a state where this high-pressure brake fluid is not expelled, high pressure is applied to the master cylinder M/C at the time of normal braking operation, and there exists a possibility of damaging the master cylinder M/C.
Additionally, in a case where the SM valve and the valves V1 and V2 are switched to release the high-pressure brake fluid to the low-pressure side in the foregoing manner after termination of traction control, the hydraulic-pressure differential of the low-pressure side and high-pressure side is large, and so oil-shock noise was generated particularly on the master-cylinder side which has small capacity, and there was considerably unpleasantness for the driver.